1. Field of the Invention
The present invention relates to an area array semiconductor device and an electronic circuit board utilizing the same, and more particularly to prevention of bending of the area array semiconductor device at a soldering operation with solder of a high melting point.
2. Related Background Art
Portable instruments such as a mobile telephone or a video camera have recently advanced in functions and become compact, and various semiconductor devices used therein are required to be thinner and compacter. As a package structure for various multi-pin semiconductor devices for meeting such requirement, there is proposed an area array semiconductor device having a ball grid array (hereinafter, referred to as “area array”) composed of plural projected solder balls arranged on a surface in a grid pattern as connection terminals.
In such area array semiconductor device, after a semiconductor chip is electrically connected to a circuit wiring substrate having a circuit wiring (hereinafter, referred to as “interposer”), the semiconductor chip is sealed with a sealant for avoiding contamination and moisture. The sealant can be composed of a ceramic material or a plastic material, but there is widely employed a package formed by a transfer molding method from a plastic material in consideration of mass producibility and cost.
The area array semiconductor device sealed with the plastic material is usually soldered to a host circuit wiring board (hereinafter, referred to as “mother board”) represented by a glass-epoxy resin wiring board. For such soldering, there has been employed a lead-containing lead eutectic solder with a melting point as low as 183° C. , thus providing the area array with a relatively small thermal stress and not causing a major problem.
However, because of recent environmental concern, use of lead-free solder, not containing lead, is being strongly requested and is rapidly increasing.
Such lead-free solder, requiring a melting point as high as about 220° C. for a high reliability of connection, increases the thermal stress applied to the area array semiconductor device. Because of this fact, the bending of the area array semiconductor device generates at the soldering operation to the mother board, whereby a solder bridging is generated to deteriorate the reliability of soldered connection. Also such defects results in an increase in the cost.
One of the most effective methods for avoiding such problem is to match a thermal expansion coefficient of the interposer with the thermal expansion coefficient of the sealing resin (hereinafter, referred to as “molding resin”) provided for protecting the area array semiconductor device from contamination or moisture. However it is difficult to match the thermal expansion coefficients because the former and latter materials are different not only in the composition but also in the configuration.
In such area array semiconductor device, an IC chip is mounted on the interposer, and, after bonding terminals of the IC chip and connection terminals of the interposer with metal wires, a molding is generally executed with a molding resin for protection from contamination and moisture and also for thermal protection. FIG. 2 shows a conventional product paying attention particularly to heat and moisture, and a molding resin 13 is molded with a relatively larger thickness in a state close to the size of the interposer (substrate) 10.
In thus molded area array semiconductor device, because of the differences in the materials and configuration of the interposer and the molding resin, both thermal expansion coefficients are different, whereby the bending of the device is generated by the heat at the soldering operation.
In the conventional soldering with the lead eutectic solder, the soldering temperature is relatively low to thereby cause only a little difference in the thermal expansion between the interposer and the molding resin, whereby the generation of bending of the device is suppressed.
In recent years, because of the requirements for the functions of the products, there are being utilized devices having large package sizes and the device having small package sizes but having small pitches of connection.
However, because of the environmental concern, the solder material is changed from the lead eutectic solders of low melting points to the lead-free solders of high melting points, and such change is causing an increase in the soldering temperature, thus resulting in the bending of the area array semiconductor device and generating a solder bridging phenomenon in the soldering operation of the area array semiconductor device.
The present invention, which has been made in consideration of the foregoing situation, is to provide an area array semiconductor device in which a molding resin is angled with respect to each side of an external periphery of an interposer so that the entire surface of the interposer is sealed by the molding resin, namely a packaging is effected in such a manner that a corner portion of a sealing layer composed of the molding resin is positioned on each side of the interposer, to reduce a contact area of the interposer and the molding resin, and to eliminate the difference in the thermal expansion of the two, thereby suppressing the bending of the area array semiconductor device, eliminating the solder bridging defect and achieving a high soldering reliability.